The present invention relates generally to apparatus for the production of foundry molds and more particularly to a molding machine within which simultaneous free-fall jolting and squeezing of the foundary molds may be effected.
Prior art techniques for the production of foundry molds are known wherein the molds are produced by compacting the molding sand by means of squeezing or trough jolting and subsequent squeezing. It is also known to produce molds by jolting with subsequent impact squeezing or through jolting with simultaneous squeezing.
Experience has shown that the most economical approach to the production of foundry molds is to employ a technique wherein the granular molding material is compacted by squeezing only. The disadvantage of this type of production method involves the fact that the compaction above the patterns which are utilized is generally too high while compaction in the parting plane of the molds is relatively low. Particularly, it has been found that the compaction is insufficient between the patterns and at the edges of the mold in the parting plane.
If the production technique utilized involves compaction of the granular molding material by jolting only, experience has shown that the compaction which results is generally inadequate. The most common practice therefore is to produce the foundry mold by compacting it by means of a process which involves a first jolting operation and a finish-compacting step with squeezing or impact squeezing occurring in a subsequent operation. The term impact squeezing ramming is generally used to indicate that, during the squeezing operation, impact forces are simultaneously imparted to the mold by means of a shaker piston either upon the pressure plate of the apparatus, the mold table or the mold table and the pressure plate. However, the granular molding compound being compacted generally does not vary its state of motion or its rest condition. In this connection reference is made to U.S. Pat. No. 1,814,416.
Such a molding technique also evinces considerable differences with regard to the compaction of the granular compound. Once again, a very high compaction of the mold material may be found to exist above the pattern while the compaction exhibited in the area of the parting line of the mold greatly decreases. Particularly, such decreased compaction is found to exist between patterns and, as a consequence thereof, the degree of utilization of the mold area is lessened because, in order to improve the compaction between the patterns, pattern spacings must be selected to be greater than desired.
It has been found that an optimum compaction of the granular compound may be achieved when the compound is precompacted by jolting in a first operation and subsequently compacted in a second operation which involves simultaneous jolting and squeezing. This production method not only results in a more uniform compaction of the granular material, particularly along the edges of the parting plane, but is also permits the selection of smaller spacings between the pattern on the pattern plate thereby considerably improving the utilization of the mold surface.
Prior art attempts have been made to compact the granular material through simultaneous jolting and squeezing wherein, while jolting, a pressure is simultaneously exerted on the granular compound by means of a juxtaposed press. This is shown in British Pat. No. 571,188. It is then necessary to select a lifting power for the jolter piston which is great enough to enable it to lift, in addition to the weight of the mold table and the parts connected therewith, the pressure additionally exerted upon the granular compound. However, although simple in its structure, the aforementioned device for simultaneously jolting and squeezing has been found to be incapable of satisfactory utilization because of the dropping motion substantially exceeds the gravity acceleration occurring during the jolting operation. Consequently, all the parts not firmly connected to the jolter table, such as the mold box, the filler frame, etc., will tend to lift off the mold table during the jolting operation.
A molding machine which effects a jolting operation and which includes a press is also known wherein the press device is supported by the jolter table for the purpose of effecting jolt-squeezing. The press is mounted to a swivelling crosspart supported by a column on the jolter table, and the swivelling crosspart with the press can be swung into a working position above the jolter table subsequent to placement of the mold blocks in position and filling the granular compound thereinto. A tension rod linked to the jolter table when the crosspart is swung in place forms a gantry over the jolter table for the absorption of pressure. In this device which is disclosed in German Pat. No. 531,024, the tension rod is disposed on the opposite side of the press relative to the column. It has been found that this molding machine adapted for simultaneous jolting and squeezing of the mold has not proven to be a practical arrangement due to the fact that forces required for swinging the swivelling crosspart with the press in and out, and the time required for this operation, have rendered its application unacceptable.
Another molding machine is known wherein a press is disposed on an arm which can be swung out and which is mounted to a column and connected to the jolting cylinder as well as to the jolter table through a bar and a bolt. Reference is here made to British Pat. No. 350,020. Such a molding device involves disadvantages in that the pressures in order to be effective must amount to several tons even for small molds, and can no longer be transmitted in the form of an open yoke with significant overhang.
A further molding machine for jolting, squeezing or simultaneous jolting and squeezing is known wherein the press is linked to the components connected to the mold table during the squeezing operation or during the simultaneous jolting and squeezing operation only and otherwise have no physical contact with the mold table (see Swiss Pat. No. 315,945). A disadvantage of this molding machine resides in the fact that, in one application, the press must be swung out to locate the mold in place, fill in and precompact the granular compound by jolting and subsequently swing in again over the mold table for finish compacting by squeezing or by simultaneous jolting and squeezing. Accordingly, it will be seen that, in the mechanism discussed above, disadvantages similar to those which arise in connection with the devices of German Pat. No. 531,024 and British Pat. No. 350,020 are also present.
However, in another application, the aforementioned molding machine can also be constructed in a revolving arrangement with one turntable supporting several jolter units and associated jolter tables, pattern devices and mold boxes. In such an application, operations are performed in several successive stations as follows: (a) the mold box is placed on the complete pattern device, (b) the granular compound is filled in and precompacted by jolting, (c) it is finish compacted by squeezing or by simultaneous jolting and squeezing, and (d) the mold is lifted off the pattern device in a final work station. This latter application involves the disadvantage that extraordinarily large masses must be moved due to the fact that several jolter units must be provided with the pattern devices molds or mold boxes on the turntable. Accordingly, a molding machine thus designed exhibits the disadvantage of requiring a very complicated drive mechanism which must transmit high forces and which, therefore, also requires extraordinarily high investment costs with high maintenance costs during operation. It has been found that in practice the mold sizes or molding machines tend to become larger and larger. This also causes the dimensions and weights of such molding machines to become so inordinately large that they are capable of being built only by a few machine tool factories.
Accordingly, it is an object of the present invention to provide a molding machine having a simple construction and capable of automatically producing molds of faultless quality at an hourly output rate sufficient for most foundries.